Pressure actuated snap action electric switch utilizing an improved belleville spring



May 13, 1969 R. L. KENYON ET AL 3,444,342

PRESSURE ACTUATED SNAP ACTION ELECTRIC SWITCH UTILIZING AN IMPROVEDBELLEVILLE SPRING Filed Dec. 1, 1966 FORCE VERSUS 6 35 DEFLECTION CURVE30 (n \J m 20 w o a: o 0

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FORCE DEFLECTION CURVE DEFLECTION (m) R/CHARD L. KENYO/V JOHN R. BURNS-ATTORNEYS United States Patent US. Cl. 200-83 28 Claims ABSTRACT OF THEDISCLOSURE A fluid pressure actuated switch including a movable contactwhich is actuated upon deflection of a snap action Belleville spring bya flexible diaphragm.

The present invention relates generally as indicated to a pressureoperated electric switch and more particularly to a snap action switchwhich employs a Belleville spring operating in the negative spring rateportion of its forcestroke curve whereat the deflection increases as theload decreases.

It is a principal object of this invention to provide a pressureoperated electric switch of the type aforesaid, which maintains a highdegree of accuracy even during vibration and throughout a broad range oftemperature change, for example, from +300 F. to 423 F.

It is another object of this invention to provide in a snap actionswitch a novel form of flexure pivoted Belleville spring which virtuallyeliminates friction and which provides for mass balancing thus toachieve true snap action with high vibration resistance and to achieveexceptional accuracy and repeatability with predictable performance andwithout first cycle stick.

It is another object of this invention to provide a pressure operatedelectric switch having calibration and system capsules arranged inseries and equalized so that the switch will be actuated bypredetermined pressure whether introduced in the calibration capsule orin the system capsule whereby operation of the switch may be checked bypressure in the calibration capsule from any convenient source withoutrequiring operation of the fluid system.

It is another object to provide a negative rate spring assembly foreffecting snap action of the switch element wherein the spring rate ofthe assembly may be accurately adjusted with the use of parts that donot require high dimensional accuracy. This is accomplished by arrangingone or more high positive rate springs (herein called a complier) inseries with a low negative rate spring so that relatively largevariations in the rate of the complier due to relatively widedimensional tolerances will result in only small changes in the negativerate of the spring assembly.

It is another object of this invention to provide a pressure operatedelectric switch which as aforesaid is temperature compensated toaccurately maintain its set point over a wide range of temperatures.

It is another object of this invention to provide a pressure operatedelectric switch in which the entire assembly of moving parts is massbalanced to minimize response to acceleration and environmentalvibration.

It is another object of this invention to provide a pressure operatedelectric switch having novel means for adjusting the preload anddeflection of the Belleville spring.

It is another object of this invention to provide a pressure operatedelectric switch which has only a minute onoff differential which is onthe order of 2% of the maximum pressure setting and in which therepeatability is on the order of 0.1% for any given environmentalcondition.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail a certain illustrativeembodiment of the invention, this being indicative, however, of but oneof the various ways in which the principle of the invention may beemployed.

In said annexed drawings:

FIG. 1 is a cross section view of a pressure operated electric switchembodying the present invention;

FIG. 2 is a bottom plan view as viewed upwardly along the line 2-2, FIG.1;

FIG. 3 is a fragmenetary cross section view taken substantially alongthe line 3-3, FIG. 1;

FIG. 4 is an enlarged fragmentary cross section view of a novel form ofBelleville spring employed in the present switch showing the same in itsdeflected switch actuating condition;

FIG. 5 is a typical force-stroke diagram of the Belleville springherein; and

FIG. 6 is a graph illustrating the snap action of the switch herein.

Referring now in detail to the drawings, the pressure operated switch 1herein comprises a housing 2 having therein: (1) a fluid pressuresensing assembly 3 including calibration and sensing capsules 4 and 5 inseries providing respective calibration and system pressure sensingports 6 and 7; (2) a spring assembly 8; and (3) a switch assembly 9.

Fluid pressure sensing assembly 3 As best shown in FIG. 1, thecalibration capsule 4 comprises a body 10 secured as by welding to thehousing 2, and a corrugated metal diaphragm 11 peripherally secured asby welding t0 the flange of said body 10 and defining therewith achamber 12 into which fluid under pressure is adapted to be introducedthrough the calibration port 6 and adjustable stop screw 15; the stopscrew 15 being abuttingly engaged by the fitting 16 fixed to the centerof said diaphragm 11 when the switch 1 is actuated by pressure in thesystem capsule 5.

The fitting 16 has a telescopic lit and abutting engagement with thebody 17 of the system capsule 5 for centering the capsules 4 and 5 withrespect to each other and for moving the body 17 when fluid underpressure of mag nitude suflicient to deflect the diaphragm 11 isintroduced into the chamber 12. The body 17 has a corrugated metaldiaphragm 18 peripherally secured thereto as by welding to define achamber 19 which is communicated with the system port 7 of the housing 2through a tube 20 which has a spring rate so small in comparison withthe spring rate of the diaphragm as to have negligible effect on thespring rate of the diaphragm 18. The body 17 also has a stop screw 21which cooperates with the fitting 23 at the center of the diphragm, saidfitting being engaged with complier plates 2425 which, in turn, areengaged with the bridge portion 26 of a force and motion transmittingring 27, the latter being engaged with a Belleville spring 13 and beingcoupled to the switch assembly 9.

The diaphragrns 11 and 18 of the calibration and sensing capsules 4 and5 are preferably of equal diameter, thickness, and material so as tohave equal spring rates whereby if there is a gap between the stop screw21 and the fitting 23 of the sensing capsule 5 there should also be alike gap between the stop screw 15 and fitting 16 of the calibrationcapsule 4 and thus when fluid under pressure is introduced into thecalibration chamber 12, the deformation of the calibration diaphragm 11will move the body 17 of the sensing capsule 5 downwardly to engage thestop screw 21 with the fitting 23, whereafter the sensing capsule willmove downwardly in unison to apply downward force and motion on thecomplier plates 24-25, Similarly, when the calibraton chamber 12 isvented and fluid pressure is admitted into the system sensing chamber19, the body 17 of the sensing capsule 5 and the fitting 16 of thecalibration capsule 4 will move upwardly until the fitting 16 abuts theadjusting screw 15 whereupon the fitting 23 of the sensing capsule 5will apply downward force and motion on the complier plates 24-25.

When the pressure switch 1 is connected, for example, to a large tank,it is often impractical, time-consuming, and expensive to pressurize theentire tank merely to test the pressure switch 1 to be sure that it isoperating properly and, therefore, in the present case, the pressureswitch 1 is provided with a calibration port 6 which actuates thediaphragm 11 which has the same characteristics as the system diaphragm18. Thus, when predetermined pressure is introduced into the chamber 12behind the calibration diaphragm 11 its central fitting 16 is forceddownwardly to actuate the system capsule 5 downwardly with the sameforce as through desired system pressure were in the system chamber 19.In this way, the operating characteristics of the pressure switch 1 maybe checked without having to pressurize the tank or other unit to whichthe system port 7 is connected for normal operation of the pressureswitch 1.

If both capsules 4 and 5 have identical preloads and effective areas,then that would obviously produce equal actuation pressures. Inaddition, if they had equal spring rates, then the on-ofl dilferentialswould be the same. Of course, manufacturing variations inevitably causethe preloads, and eflective areas to be unequal. As previously pointedout, there are positive stops 15 and 21 in the respective capsules 4 and5 which provide means for adjusting these variations. These positivestops 15 and 21 may, but do not have to be, in contact with respectivecenter fittings 16 and 23 when the pressure switch 1 is in theunpressurized state. It is only necessary when the system port 7 ispressurized that the calibration capsule 4 bottoms against its stop 15before the pressure switch 1 actuates, Similarly, when the calibrationport 6 is pressurized it is necessary that the system capsule 5 bottomsagainst its stop 21 before the actuation pressure is reached. With equalspring rates, equal preloads require equal defiections of the capsules 4and 5 from their free position. This deflection consists of twocomponents, i.e., the deflection of the capsule 4 or 5 in the installedand unpressurized state and the additional deflection thereof whenpressurized to actuation pressure. Because the capsules 4 and 5 are inseries they will exert equal axial forces assuming that neither internalstop 15 nor 21 is bottomed. Each capsule 4 and 5 must, therefore,experience additional deflection when it alone is pressurized in orderthat the preload force of the system capsule 5 will be the same when itactuates the pressure switch 1 as the preload force of the calibrationcapsule 4 when it actuates the pressure switch 1. This means that in theinstalled unpressurized state, each capsule 4 and 5 will have an equalgap at its internal stop 15 and 21.

In practice, the positive stop 21 of the system capsule 5 is preset sothat it will bottom out at a small percentage of the actuation pressure,The positive stop 15 of the calibration capsule 4 is adjusted to makethe system and calibration actuation pressures identical. Then, theentire spring assembly 8 hereinafter described will be adjusted todeflect both capsules 4 and 5 simultaneously a distance sufficient togive the exact preloads that produce desired actuation pressure. As apractical matter, the manufacturing variations in the diaphragms 11 and18 are not of suflicient significance as to make necessary anyadjustment for unequal spring rates thereof. The variations in preloadand effective area are taken care of as described above.

4 Spring assembly 8 The spring assembly 8 includes a negative rateBelleville spring 13 and positive rate complier spring plates 24, 25arranged in series. Spring 13 is fabricated from a single piece ofspring metal which has a rigid circular base 30 located coaxially withinthe housing 2 by reason of its close fit over the upstanding annularboss 31 of a ring 32 disposed in an adjustable carrier 34. Between thecircuit base 30 and the ring 32 there may be a spacer shim 35 foradjusting the initial deflection and hence the preload of Bellevillespring 13 and both the shim 35 and the Belleville spring 13 are keyedagainst rotation with respect to the ring 32 as by means of the dowellpin 36. Extending vertically from the base 30 are a circular series offlexible columns 37 which may be radially thickened, as shown, wherethey join the circular base 30 and the Belleville spring portion 38, thelatter being in the form of a coned or dished washer. Extending upwardlyfrom the Belleville spring portion 38 at a diameter smaller than thejuncture of the lower columns 37 are another circular series of flexiblecolumns 39 which may also be radially thickened as shown, when joined tothe Belleville spring portion 38 and to the upper rigid ring portion 40.

Telescoped within and abutting the upper ring portion 40 is the forceand motion transmitting ring 27 to the bridge 26 of Which force andmotion is transmitted from the system capsule 5 or from the calibrationcapsule 4 as previously mentioned through the intervening complierplates 24-25 The ring 27 and Belleville spring 13 are keyed together asshown to prevent relative rotation. The lower end of said bridge hassecured therein a motion transmitting rod 45 which is adjustablyconnected to the stud 46 of the movable contactor 47. The bridge 26 hasan opening therethrough which is vertically larger than the centerbarrel-shaped portion of the pin 48 which extends across the upperbifurcated end of the stop member 49, the ends of said pin beinganchored in the stop member 49.

Between the ring 27 and the system capsule 5 are the so-called complierplates 2425 through which movement of the system capsule 5, either bypressure in the calibration chamber 12 or in the system chamber 19, istransmitted to the ring 27 to the upper ring portion 40 of theBelleville spring 13.

In the present case the Belleville spring 13 is of negative rate and isused to provide a negative spring rate for spring assembly 8 to causesnap-action operation of the switch element. Of course, the magnitude ofthe negative spring rate of spring assembly 8 will determine the on-otfdifferential of the pressure switch 1. The purpose of the complier 2425is to provide a precise, convenient, and practical method of adjustingthe negative rate of the spring assembly 8 so that the pressure switch 1will have the desired on-off differential. Adjustment is necessarybecause Belleville spring 13 cannot be manufactured to spring-ratetolerances so close as to preclude the necessity for individualadjustment or selection of springs where, for example, the on-otfdifferential is to be held to tolerances as close as plus or minus 1% ofactuation pressure.

Because complier '24-25 is a positive rate spring in series with thenegative rate Belleville spring 13, decreasing the rate of the complier24-25 increases (makes more negative) the negative rate of the assembly.However, the complier 24-25 is quite stifi, that is, of high rate, ascompared to the Belleville spring 13 and because of this, large changesin complier 2425 spring rate cause only small changes in spring rate ofthe assembly. It is therefore easy to establish the desired negativerate of the assembly within close limits by pairing an appropriate setof complier plates 24, 25 with a given Belleville spring 13. As shown,the complier 24-25 is simply a pair of flat metal plates 24 and 25nested one within the other, the spring rate of which is varied byvarying the plate thickness.

With any given Belleville spring 13, complier plates 24, 25 from arelatively wide thickness range may be used and still have the negativerate of the assembly fall within the desired close range and thus thecompliers need not be manufactured to close tolerances. Where thecomplier 2425 contacts other pressure switch parts or contacts othercompliers as shown, a thickened rim or hub is provided as shown toprevent deflections at the points of contact which could introducefriction forces detrimental to the accuracy of the pressure switch 1.

With reference to temperature compensation, in order to cancel out thechange in setting caused by temperature, a compensating change insetting is introduced by changing the deflection of the sensing capsule5 with temperature. Because the sensing capsule 5 has a high positiveconstant spring rate, small changes in sensing capsule 5 deflection willcause the required compensatory pressure setting change. This is done byrepositioning according to temperature, the entire spring 8-positivestop 4849 assembly which is, in effect, a self-contained module whichrests on a device which may be called a thermal compensator comprisingan Invar ring 50 mated with a steel or aluminum ring 51 and thewedge-shaped cross section of the rings 50 and 51 together with thedifference in coeificients of thermal expansion thereof causes theheight or thickness of the said compensator to vary with temperature ina controlled manner.

A snap action pressure switch 1 which actuates at a certain pressure aspressure is increased, will deactuate or snap back to the original stateat a pressure level which is always lower than that required to causeactuation. This difference between actuation pressure and deactuationpressure is necessary in order to store energy to power the snap actionswitching. This difference is the on-oif differential and the magnitudethereof depends on the net negative spring rate of the pressure switchmechanism and, therefore, depends on the negative spring rate of thespring assembly 8. Because the force-deflection curve of spring assembly8 is not a straight line (see FIG. 5), the effective spring rate dependson the location of the positive stops 4849 for spring assembly 8 betweenwhich it operates the pressure switch. If changes in temperature Werepermitted to change the location of the positive stops 48-49 relative tothe spring assembly 8, this would change the effective negative springrate of the spring assembly 8 and would, in turn, result in a change inon-otf differential. The typical force deflection curve shown in FIGS. 5and 6 shows how rapidly the spring rate can change for even a fewthousandths inch change in positive stop position. The positive stops4849 for the spring assembly 8 therefore are located in the closeproximity to the spring assembly 8 and the entire spring 8-positive stop48-49 assembly is designed as a self-contained module constructed frommaterials having substantially identical coeflicients of thermalexpansion. Despite temperature changes, this keeps the positive stops48-49 at the same relative location on the spring assembly 8force-deflection curve. This feature substantially simplifies the taskof insuring that pressure switch performance does not vary withtemperature. In FIG. 6 the dotted lines show the snap action motion ofthe flexure pivoted spring assembly 8 installed between positive stops(left curve without electrical contactor forces and right curve withelectrical contactor forces.)

Accordingly, one of the novel features of the present pressure switchtemperature compensation arrangement is the use of the wedge typecompensator rings 50 and 51 to provide the compensating movement andembodying such compensating movement of the entire spring 8-positivestop 48-49 assembly so as to leave the spring assembly 8 centered in thesnap action region while obtaining the compensation from the change insensing capsule 5 preload.

Switch assembly 9 Secured as by welding in the lower end of the housing2 is a cap 55 to which is welded an electrical receptacle 56 havingcontact pins 57 to which switch leads are connected as shown. As bestshown in FIGS. 1 and 2, the movable contactor 47 is mounted at one endon posts 58 between insulating sleeves for flexing in the manner of acantilever beam and having weakened flexible sections adjacent theintermediate actuator stud 46. The free end of the flexible contactor 47is provided with contacts 59 which alternately engage the normallyclosed and normally open contacts 60 and 61, respectively, said contacts60 and 61 being mounted on screw posts 62 between insulating sleeves. Ashereinafter described, the flexible contactor 47 is preferably preloadedwhen in the FIG. 1 position, and when the pressure switch 1 is actuated,the normally open contact 61 is similarly engaged by contact 59 withload on the contactor 47. In this way, the switch contacts 59 and 60 or59 and 61 will remain in engagement despite environmental vibration ofthe pressure switch 1 and moreover, the spring contactor 47 has a highnatural frequency and is mass balanced further to resist contact chatterunder conditions of vibration.

The switch plate 63 which carries the spring contactor 47 and the fixedcontacts 60 and 61 is bolted to the ring 32 which has the upstandingannular boss 31 around which the Belleville spring 13 is coaxiallydisposed and within which is seated the stop member 49.

Between the switch plate 63 and the inturned flange of the carrier 34are the previously referred to temperature compensating rings 50 and 51.As can be seen, the stop pin 48 and stop member 49 and base 30 of theBelleville spring 13 may be adjusted toward or away from the systemcapsule 5 by rotary adjustment of the carrier 34, the latter beinglocked in adjusted position as by means of the lock nut 64 which hasthreaded engagement with said carrier 34 and which is seated against ashoulder 65 in the housing 2. Furthermore, when the cap 55 is welded inplace, it further engages the lock nut 64.

Adjustment of the contacts 59 so as to exert contact load on contact 60and on contact 61 may be effected as by removing the screws 67 androtating the switch plate 63 in angular increments corresponding toscrew hole spacing which causes the stud 46 to be screwed into, orunscrewed from, the motion transmitting rod 45.

Operation In normal operation of the pressure operated electric switch 1herein the system pressure enters the chamber 19 through the system port7 and the tube 20 and applies a downward force on the system diaphragm18 and an upward reaction force on the body 17 to deflect thecalibration diaphragm 11 until the fitting 16 engages the positive stopscrew 15. The downward force is transmitted by complier 24, 25 to theBelleville spring 13 through the ring 27 which bears downwardly on theupper ring portion 40 of said Belleville spring 13. When the systempressure equals the switch actuation pressure, the downward forcedeflects the Belleville spring 13 and compliers 24, '25. Because the netspring rate of the spring assembly is negative, the downwardaccelerating force increases as the system capsule 5 expands downwardly.As a result, the motion is a snap action to the FIG. 4 condition of theBelleville spring 13 'whereat the bridge 26 opening engages the uppersurface of the stop pin 48. At that stop position the rod 45 will haveflexed the movable contactor 47 to engage the contact 59 with normallyopen contact 61 with a desired contact load.

When the pressure switch 1 is used in its normal manner wherein thesystem capsule 5 senses system pressure in port 7, the calibration port6 is vented to ambient pressure. The system pressure in the chamber 19exerts a substantial holding force on the calibration diaphragm 11 byengagement of the fitting 16 thereof with the stop screw 15. Becauseneither system pressure nor acceleration forces due, for example, tovibration, can pull the calibration diaphragm 11 away from its stop 15,such pressure or vibration cannot influence normal switch operation.

When it is desired to check the operation of the pressure switch 1without having the system in operation, switch actuation pressure isapplied in the calibration chamber 12 whereupon the calibrationdiaphragm 11 deflects downwardly with consequent engagement of stopscrew 21 with fitting 23. Downward force on the compliers 24-25 and onthe ring 27 again, as above-described, deflects the Belleville spring 13to effect switch actuation.

Summary The Belleville spring portion 38 herein is supported by flexurecolumns 37 and 39 which, as aforesaid, are preferably machined integralwith the Belleville spring portion 38, said flexure columns 37 and 39having the advantage of providing a flexure supported Belleville springwith elimination of mechanical friction. Another advantage of theintegral one-piece unit constituting the Belleville spring 13 is thattesting thereof is possible on its supports 32 and 27 prior to assemblywith the sensing assembly 3 and the switch assembly 9. The flexurecolumns 37 and 39 are spaced to provide a flexure support and aredimensioned to impart minimum end moments to the Belleville springportion 38 during flexure of the latter. By arranging the -flexurecolumns 37 and 39 circularly, as shown, there is provided an inherentlyri id construction that resists transverse loading in all directions byplacing the long width of approximately onethird of the columns inalmost pure shear. As best shown in FIG. 4, the flexure columns 37 and39 are placed to operate the Belleville spring portion 38 in the mannerof a lever having a fulcrum at 68 so that the moving masses on each sideof said fulcrum 68 counterbalance each other. The lever ratio isselected depending on the desired pressure setting.

Another consideration is that mechanical friction and hysteresis aresources of error in devices of this type. In the present case,mechanical friction is nil and internal hysteresis in the stressedmembers is minimized by keeping the stresses in critical members low. Inknown Belleville spring support systems using c nventional pivots, thefriction is about 1 /2%, whereas mechanical friction is eliminated inthe present switch 1. The importance of this is revealed by the factthat in numerous consecutive cycles the repeatability is within 0.1%,because there are no sliding or rolling contacts and instead only theelastic flexure of the thin strips of the flexure columns 37 and 39which preferably have a low spring constant in the desired direction offlexure and a very high spring constant for movement in otherdirections.

Another undesirable characteristic of known pressure switches is oftenreferred to as first cycle stick which, as the term implies, requiresapplication of increased switch actuation force the first time that theswitch is actuated. With the present switch 1 first cycle stick iseliminated by the frictionless flexure pivoted Belleville spring 13.Even in tests wherein the pressure switch 1 herein was cooled to -320 F.there was complete absence of first cycle stick.

By way of illustrative example, a pressure switch 1 in accordance withthis invention may employ a Belleville spring 13 in which there aresixteen flexure columns 37 and 39 of about 0.0007" radial thickness andof about 0.130" in length in each of the lower and upper sections of theBelleville spring 13.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims, or the equivalent ofsuch, be employed.

We therefore particularly point out and distinctly claim as ourinvention:

1. A fluid pressure operated electric switch comprising a housing havingtherein: switch means with a movable contact; a Belleville springoperatively engaging said contact to actuate said switch means upondeflection of said spring between the inner and outer periphery thereof;said spring having radially spaced apart axial projection on oppositesides; support means engaging the projections on one side of saidspring; and fluid pressure actuated means for applying axial force tothe projections on the other side of said spring to deflect said spring,said projections being radially spaced from one of said peripherieswhereby said spring is thus deflected by lever action.

2. The switch of claim 1 wherein said fluid pressure actuated meanscomprises a pressure capsule and means for introducing fluid underpressure thereinto; said capsule comprising a flexible diaphragm whichexerts axial force on said spring upon introduction of fluid pressureinto said capsule.

3. The switch of claim 25 wherein said capsules have respective firstand second axially adjustable stops means engaged by the respectivediaphragms and backed up respectively by said housing and by said firstcapsule whereby when said first diaphragm is axially deformed asaforesaid it applies axial force on said spring through engagement ofsaid second stop means with said second diaphragm and when said seconddiaphragm is axially deformed as aforesaid it applies axial force onsaid spring while said second capsule is backed up by engagement of saidfirst stop means with said first diaphragm.

4. The switch of claim 26 wherein said portions are a fixed part of saidspring.

5. The switch of claim 26 wherein said portions are disposed inconcentric circles.

6. The switch of claim 5 wherein said portions are a fixed part of saidspring and comprise circumferentially spaced apart columns.

7. The switch of claim 6 wherein said columns are relatively thinradially so as to flex to arched form as said spring is deflected.

8. The switch of claim 7 wherein said columns are integral with saidspring; said columns being integrally joined at their ends axiallyremote from said spring to continuous rings; one of said rings beingengaged with said support means and the other of said rings having suchaxial force applied thereto.

9. The switch of claim 27 wherein said temperature compensating meanscomprises a pair of juxtaposed rings having mating frusto-conicalsurfaces, one ring having a substantially smaller coeflicient of thermalexpansion than the other ring whereby radial expansion or contraction ofthe latter due to temperature change is reflected as a change in thecomposite axial thickness of said rings according to the apex angle ofsuch frusto-conical surfaces.

10. The switch of claim '1 wherein said Belleville spring has a forcevs. deflection curve of which a portion is of negative slope to effectsnap-action actuation of said switch means.

11. The switch of claim 28 wherein said complier comprises at least oneplate of which the center portion deflects relative to the peripheralportion under switch actuating load.

12. A Belleville spring adapted for use in a fluid pres sure operatedswitch and the like comprising a frustoconical ring portion, andradially spaced apart axial projections on opposite sides of said ringportion through which opposite axial forces are adapted to be applied tosaid ring portion to deflect it to a greater apex angle and to a shorteraxial distance between the inner and outer peripheries thereof, saidprojections being radially spaced from one of said peripheries wherebysaid spring is thus deflected by lever action.

.13. The Belleville spring of claim 12 wherein said projections lie onconcentric circles which are coaxial with said ring portion.

14. The Belleville spring of claim 12 wherein said projections are afixed part of said ring portion.

15. The Belleville spring of claim 12, wherein said projectionscomprises circumferentially spaced columns on opposite sides of saidring portion.

16. The Belleville spring of claim 15 wherein said columns are joinedwith continuous ring means at their ends axially remote from said ringportion whereby axial forces are applied on said ring portion throughsaid means.

'17. The Belleville spring of claim 16 wherein said columns are integralwith said ring portion and with said ring means and are of relativelysmall radial thickness so as to flex to arched form as such axial forcesare applied to said ring portion.

18. The Belleville spring of claim 17 wherein said columns are radiallythickened where joined to said ring portion and to said ring means.

19. Snap-action mechanism for a fluid pressure actuated electric switchand the like comprising a Belleville sprin-g adapted when deflected byaxial force thereon to actuate such switch; support means engaging oneside of said spring; said spring having a force vs. deflection curvewhich is characterized by having a portion of negative slope; stop meanson said support effective to pre-load said spring to an extent near thetransition of said curve from positive slope to negative slope and torestrict further deflection so as to be in the negative slope portion ofsaid curve; and fluid pressure actuated means applying axial force onthe other side of said spring at a zone radially spaced from saidsupport means; said axial force, when of magnitude exceeding suchpre-load on said spring, producing snap-action deflection of said springwith corresponding snap-action actuation of a switch and the likeadapted for actuation by said spring.

20. The snap-action mechanism of claim 19 wherein said spring hasintegral circular series of radially thin columns which project axiallyin opposile directions and which are integrally joined to continuousring portions at their ends axially remote from said spring; saidcolumns being flexed to arch form when said spring is pre-loaded andsubsequently deflected thus to provide a flexure pivoted spring thateliminates mechanical friction.

2 1. The snap-action mechanism of claim 19 wherein a complier isinterposed between said Belleville spring and said fluid pressureactuated means; said complier being a positive rate spring having asubstantially greater rate than said Belleville spring whereby thecombined rate of said complier and Belleville spring is diflerent fromthe rate of the latter.

22. The snap-action mechanism of claim 21 wherein said compliercomprises at least one plate of which the center portion deflectsrelative to the peripheral portion under switch actuating load.

23. A fluid pressure operated electric switch comprising a housinghaving therein: switch means with a movable contact; a Belleville springoperatively engaging said contact to actuate said switch means upondeflection of said spring; support means engaging one side of saidspring; and fluid pressure actuated means applying axial force on theother side of said spring at a zone radially spaced from said supportmeans to deflect said spring by lever action; the moving parts of saidspring and said fluid pressure actuated means defining a substantiallymass-balanced assembly thus to minimize response of said switch tovibration.

24. The switch of claim 23 wherein said movable contact is mass balancedand has a relatively high natural frequency further to resist chatterunder conditions of vibration of said switch.

25. A fluid pressure operated electric switch comprising a housinghaving therein: switch means with a movable contact; a Belleville springoperatively engaging said contact to actuate said switch means upondeflection of said spring; and fluid pressure actuated means forapplying axial force to deflect said spring; said fluid pressureactuated means comprising first and second axially adjacent pressurecapsules and first and second means for introducing fluid under pressureinto the respective capsules; said capsules comprising respective firstand second flexible diaphragms which, in the case of said firstdiaphragm, exerts axial force on said spring through said second capsuleupon introduction of fluid pressure into said first capsule and which,in the case of said second diaphragm, exerts axial force directly onsaid spring upon introduction of fluid pressure into said second secondcapsule.

26. A fluid pressure operated electric switch comprising a housinghaving therein: switch means with a movable contact; a Belleville springoperatively engaging said contact to actuate said switch means upondeflection of said spring; support means engaging one side of saidspring; and fluid pressure actuated means applying axial force on theother side of said spring at a zone radially spaced from said supportmeans to deflect said spring by lever action; said spring havingopposite axially ext-ending portions constituting said support means andaxial force transmission means through which such axial force is appliedon said spring.

27. A fluid pressure operated electric switch comprising a housinghaving therein: switch means with a movable contact; a Belleville springoperatively engaging said contact to actuate said switch means upondeflection of said spring; support means engaging one side of saidspring; and fluid presure actuated means applying axial force on theother side of said spring at a zone radially spaced from said supportmeans to deflect said spring by lever action; and temperaturecompensating means interposed between said support means and saidhousing to maintain a predetermined relation between said spring andsaid fluid pressure actuated means over a wide range of ambienttemperatures.

28. A fluid pressure operated electric switch comprising a housinghaving therein: switch means with a movable contact; a Belleville springoperatively engaging said contact to actuate said switch means upondeflection of said spring; fluid pressure actuated means for applyingaxial force to deflect said springs; said Belleville spring having aforce vs. deflection curve of which a portion is of negative slope toeflect snap-action actuation of said switch means; and a complierinterposed between said Belleville spring and said fluid pressureactuated means; said complier being a positive rate spring having asubstantially greater rate than said Belleville spring whereby thecombined rate of said complier and Belleville spring is different fromthe rate of the latter.

References Cited UNITED STATES PATENTS 2,582,483 1/1952 Hallerberg200--83.1 2,615,104 10/1952 Hosford 20083.9 2,953,658 9/1960 Davis20083.9 XR 3,036,173 5/1962 Perkins 20083.9

ROBERT K. SCHAEFER, Primary Examiner.

H. BURKS, Assistant Examiner.

